Impulse generator



April 1937. H. L. RORDEN ET AL ,773

IMPULSE GENERATOR Filed May a, 1956 OSCILLATOR INVENTORS fiar-o/a L. Pore/en BY Pau/ M. Ross A {a a f2 ATTORNE L Patented Apr. 20, 1937 UNITED STATES PATENT OFFICE 2,077,773 IMPULSE GENERATOR Application May 8, 1936, Serial No. 78,720 zociaims. (01.175-183) This invention relates to impulse generators for producing high voltage impulses and has for one of its objects the provision of an impulse generator circuit in which the voltages produced can be accurately controlled and evaluated and accurately reproduced in successive operations of the generator when so desired.

A further object of the invention is to provide a novel means for initiating series discharge of the capacitors of the generator comprising means for grounding one terminal of the series circuit.

A further object of the invention is to provide a connection between the impulse generator circuit and the circuit of a cathode ray oscillograph which provides for excitation of the cathode prior to discharge of the generator but in which the operation of the oscillograph is precipitated by the same operation which precipitates the discharge of the generator.

A further object of the invention is to provide a circuit in which the discharge of the generator and the operation of the oscillograph are initiated by the same control mechanism but in which the operation of the oscillograph is caused to begin at a predetermined and constant interaccompanying drawing and described'in the following specification, and it is more particularly pointed out in the'appended claims.

'In the drawing:

Fig. 1 is a diagram showing the circuit connections of one embodiment of the present invention.

Fig, 2 is a fragmentary diagram showing a modified arrangement of a portlonoi' the mechanism shown in Fig. 1.

Fig. 3 is a fragmentary circuit diagram showing still another modification.

In Fig. 1 of the drawing, the numerals l0, ll, I2, I, i5, i6 and I1 represent'the capacitors of an impulse generator. The impulse generator may be and preferably "is orthe general type shown in Patent No. 1,997,064, granted April 9,

1935 to J. T. Lusignan, Jr. It will be understood, however, that the present invention may be applied to various forms of impulse generators and it will also be understood that the number of capacitors connected as shown in the diagram may be extended to include the requisite number to give the desired voltage, and each of the capacitor units indicated by the above reference characters in fact include a large number of separate capacitors connected in series or in any suitable combination of series and parallel connections. The capacitor units are arranged in units or groups connected in series, as shown in the diagram, and resistances iii are arranged in the circuit of each group. These resistances may be varied as found desirable to control certain characteristics of the wave of the generated impulse. The first group of capacitors l0 and I4 are grounded through an impedance l9 at the mid point in the group.

Heretofore it has been customary to ground the endmost terminal of the series of capacitors at the point 20 but according to the present in.-

' vention, a sphere gap 2i is connected between the point 20 and ground for reasons which will be more fully explained. The several groups of capacitors are connected in multiple by conductors 22 and 23, and impedances 24, 25, 26', 21, etc. are connected in the conductors between the terminals of the various groups of capacitors. One terminal of each group is connected to the opposite terminal of the next adjacent group through sphere gaps 28. Any suitable operating mechanism, such as a motor 30, may be employed for adjusting the spacing of the gaps 28. This operating mechanism is preferably arranged for simultaneous adjustment of all of the gaps from a distance, as'more fully explained in Patent No. 1,997,064 referred to above. The end of the conductor 22 is connected through a gap 32 and a resistance 33 to ground. The resistance 33 may be of sufficient value to apply substantially the total voltage generated upon a test piece connected in parallel with the resistance. In some cases, it may be desirable to substitute the test piece for the resistance 33.

The other end of the secondary winding 38 is connected through thermionic valves 38 and 39 to the terminals 40 and II respectively of a reversing switch so arranged that the terminals of the thermionic valves may be selectively connected to the conductors 22 and 23. The valves 38 and 39 are arranged in reverse order in their circuits so as to produce a full wave rectifier for charging the capacitors of the impulse generator with the conductor 22 either positive or negative with respect to ground as desired so as to impress either a positive or negative impulse on the test piece in parallel with the impedance 33. The switch terminals 48 and 4| may be short circuited by a discharge switch 42 which is biased to a closed position but which is opened to permit charging of the impulse generator when the relay 43 is energized. The switch 42 is preferably biased to close automatically as soon as the relay 43 is de-energized. The relay43 also controls the circuit of the primary winding of the transformer 34 as indicated by the terminals 44. The terminals 44 are connected so as to complete the circuit for the primary 35 at the same time that the discharge switch 42 is open.

It will be seen that by this arrangement the several groups of capacitors will be charged in parallel and may be discharged in series by moving the lower terminal of the gap 2| into contact with the upper terminal so as to ground the circuit at the point 20. When this is done, there is a tendency for the capacitor M to discharge through the impedance l9, but due to this impedance, the combined charge of the capacitors I8 and H are momentarily connected in series and their combined voltage is impressed on the first gap 28. This causes discharge across the gap 28 and immediately the capacitors l4, l0, l5 and II are placed in series, due to the arc across the first gap 28, and their combined. voltage is applied to the second gap 28. In this way a series path is provided for all of the capacitors so that the capacitors of the entire generator 26 and 21.

discharge in series across the gap 32 and resistance 33 to ground. During this discharge, the parallel connections through the conductors 22 and 23 will be practically blocked, so far as the impulse is concerned, by the impedances 24, 25, The speed at which the impulse is built up and consequently the wave front, will be determined by the impedances l8 in series with the capacitors. Substantially the total voltage of the capacitors in'series will be impressed upon the impedance 33 and the tail of the wave will be determined mainly by the character of the impedance 33. By the arrangement shown, the capacitors of the first group are charged in two sections, due to the ground connection through the impedance l9, so that the secondary winding 36 is subjected only ,to voltage to ground equal to the voltage necessary to charge half the capacitors in the group while if the ground were permanently connected at 2|, the secondary 36 of the transformer would be required to withstand a suflicient voltage to charge the entire group in series. When the generator discharges, however, the ground is automatically shifted to the point 20 by closing .the gap at this point so that all of the capacitors are connected in series and the total impulse voltage generator is above ground potential.

The impedances I9, 24, 25, 26,21, etc., may comprise resistance alone or may include inductance'and they should be great enough to give to the various local circuits of which each is a part a time constant at least ten times that of the main series discharge circuit. It has been found in practice that with this relative value of the time constants of the circuits, practically all of the energy of the discharge impulse will be expended in the main series discharge circuit containing the test piece and the loss in the local circuits will be immaterial.

The characteristics of the impulse wave are recorded by a cathode ray oscillograph, the elements of which are diagrammatically illustrated in the drawing; the cathode being designated by the numeral 45, the anode by the numeral 46, the time deflector plates by the numeral 41, the surge deflector plates by the numeral 48, the photographic film by the numeral 49, and the adjustable impedance for controlling the voltage 'on the surge deflector plates by the numeral 50. The impedance is connected-in a circuit arranged in parallel with the impedance 33, which circuit includes a high resistance 5| and a capacitance 52 in the form of a cable having a grounded sheath through which the lead-in conductor passes. By adjusting the impedance 58, the surge deflector plates can be subjected to a suitable proportion of the surge voltage so as to deflect the cathode ray and record the characteristics of the impulse, on the fllm 49, in a well known manner.

Whenever the cathode 45 is energized and a reading is not being taken, the ray is deflected to a grounded lead cup 53 by means of deflector plates 54 which are automatically de-energized to free the ray of their influence when a reading is to be taken. The cathode 45 is charged by means of two capacitors 55 connected in series and having the secondary of a transformer 56 connected to their adjacent terminals. The other terminals of the capacitors are connected through thermionic valves 58 to the opposite terminals of the secondary of the transformer 56. This arrangement, as will be seen, provides a full wave rectifler for charging the capacitors 55 in series, the arrangement being such that the ungrounded terminal of the capacitors 55 will be negative with respect to earth. A discharge switch 63 is provided for short-circuiting the capacitors 55 when not in use, the switch being controlled by a relay 64 which also controls the primary circuit of the transformer 56. Whenever the relay 64 is energized, the switch 63 is opened and the primary circuit for the transformer 56 is closed so that the capacitors 55 are charged and their negative voltage is impressed upon the cathode 45. The deflector plates 54 and 41 are energized by capacitors 65 and 66 which are charged by means of a transformer. 61 and rectifier tubes 68 and 69. These capacitors are connected in series through resistance 10 and discharge gaps II and 12. Normally the capacitors will be prevented from discharge by the gap H and 12 so that so long as they are charged the deflector plates 54 will be energized and the. cathode ray will be diverted to the terminal cup 53, as indicated by the broken line.

Whenever the gap 2| is closed, the voltage at. the point 3| of the generator circuit will be raised so that a voltage will be impressed on thesphere between the gaps II and I2. This will increase the voltage across one or the other of the gaps II and 12 so as to induce discharge across these gaps. When this takes place, there will be a voltage impressed across the resistance 10 and the capacitor 13 paralleling this resistance, which voltage will be impressed on the deflector plates 41. This will produce a deflection of the cathode ray longitudinally of the photographic film 49 at the same time that the impulse of the genermotor starts.

ator is impressed on the test piece and on the deflector plates 48 producing a lateral deflection of the ray, showing the characteristics of the impulse-wave. The discharge of the condensers 65 and 66 will be controlled by the resistances 10, 14, 15 and the time deflection of the ray may be regulated by adjusting the condenser 13.

The transformer 34 for charging the impulse generator is energized from a motor generator 16 through a circuit provided with a disconnecting switch 11 and controlled by a relay 18. The remaining apparatus is energized from bus bars 19.

A series of timing'cams 80, 8| and 82 is provided for controlling the sequence and time of operation of the various mechanisms, the cams being driven by a motor 83 connected to the bus bars through a hand switch 84. The cam 80 controls therelay 18 which is connected to the bus bars through a hand switch 85. The cam 8| controls the solenoid 81 to close the gap 2| for firing the impulse generator. The circuit of the solenoid 81 is also connected through leads B8 to a double throw switch 89 by means of which the leads may be connected through a yard line to a camera trained upon the test piece. When the switch is closed to connect the camera with the solenoid 81, the camera shutter will be opened simultaneously with the discharge of the impulse generator so that a synchronized photograph of the discharge will be taken. By throwing the switch 89 in the other'direction, the yard line may be connected with the bus bars 19 to provide a source of voltage for any desired use in the test .cam 82 controls the circuit of an alarm 9| connected with the bus bars by a hand switch 92. The solenoid 43 is connected to the bus bars through a hand switch 93. The rectifier valves 38 and 39 are connected to the bus bar through leads 94 and hand switch 95. The rectifier valves 58 are energized by a transformer 96 having separate secondaries for the two valves and a common primary connected to the bus bars by a hand switch 91. It has been found convenient to enclose the transformers 56 and 96 in a single housing not shown. The relay 64 for controlling the operation of the transformer 56 which charges the capacitors and also for controlling the short circuit of these capacitors is connected to the bus bars through a hand switch 98. The transformers.for energizing the rectifier valves 68 and 69 are connected to the bus bars by a hand switch 99. The transformer 61 which energizes the capacitors and 66 is connected to the bus bars by a hand switch I00. A vacuum pump |0I for the oscillograph is connected to the bus bars through a hand switch I02 and an oscillator I03 for supplying the time reference curve to the oscillograph is connected to the bus bars by a hand switch I04. During operation, the various hand switches are kept closed, except the switch 84 which controls the timing motor 83.

When it is desired to start a series of operating cycles, the switch 84 is closed and the timing The cam first closes a switchwhich energizes the relay 18 to begin charging of the capacitors of the impulse generator. After a sufficient time has elapsed to charge the generator .capacitors, the cam 82 closes the alarm circuit and causes the bell 9| to ring, so that all persons present will be notified that the generator is about to discharge. A short period after the sounding of the alarm, the cam 8| will close the circuit of the solenoid 81 which will close the gap erably located adjacent the gap terminal.

\ 2| and impress the impulse wave of the generator upon the resistance 33 and the test piece in parallel therewith. Since the hand switches 91 and 98 have previously been closed, the cathode 45 will be charged prior to the discharge of the generator and since the switches 99 and I00 are also closed, the capacitors 65 and 66 will be charged and the cathode ray will be deflected to the cup 53. As soon as the gap 2| is closed, voltage will be impressed upon the central sphere between the gaps 1| and 12, inducing an are at this point and closing the discharge circuit of the capacitors 65 and 66, thus restoring the cathode ray to its operating position and energizing the time deflector plates 41 in a mannerpreviously described. Since there is a time lag in the discharge of the impulse genera tor, the time deflection of the oathode ray will begin just before the discharge of the generator takes place so that a record will be made of the entire impulse wave. An insulating capacitance I05 is interposed in the circuit between the point 3| and the central terminal of the gaps 1| and 12, the capacitance being prefpurpose of this capacitance is to exclude the high voltage of the capacitor I4 from circuits which are handled by the operator.

If it is desired to increase the time lagbetween the operation of the control circuit for the time deflector plate 41 and the discharge of the impulse generator, this may be done by reducing the size of the first pair of gap terminals 28 as shown in Fig. 2 so as to give this gap characteristics approaching that of a rod gap instead of a sphere gap. This will produce a time lag after closing the gap 2| before the first gap 28 will arc.- With this arrangement, there will be a tendency for the point I06 to vary with respect to ground potential during the time lag before the discharge of the gap 28 and subsequent to the closing of the gap 2|. This may be avoided by inserting a capacitance I01 between the point I06 and ground. It has been found in practice that a capacitance of approximately .002 microfarad at this point will give satisfactory operation.

In tests of some forms of apparatus, such as transformers, some standards require that the test piece be energized from a standard source of alternating current at the same time that it is subjected to the test impulse. form a test of this nature by the present invention, the arrangement shown in Fig. 3 may be employed in which the terminals of the gap 20 are spaced farther apart and a supplemental electrode I08 is interposed between the two gap terminals. The electrode is connected through an impedance I09 to the secondary N0 of a transformer, the primary III of which'can be connected in any suitable way, as by leads 2 and hand switch 3 to any desired source of alternating current, usually 60 cycles. The winding III is connected in parallel with the primary winding 4 of the transformer I|5 being subjected to test.

In this case the secondary H6 is connected in parallel with a potentiometer 1 made up of capacitors in series. A gap H8 is interposed in the circuit of the secondary I I6 to exclude the 60 cycle voltage from the impulse generator circuit. In this case the impulse deflector-plates 48 are connected to the terminals of an adjustable capacitor II9 connected in a divider circuit formed of a series of capac'tors I20 in parallel with the potentiometer II]. The 60 cycle voltage is impressed on the test piece and the electrode The' In order to pera I08 prior to charging the capacitors of the impulse generator. The capacitors of the impulse generator are thus gradually charged and the gap 2| is set to arc over when the charge on the generator capacitors is suflicient to produce the impulse voltage desired for the test. When the voltage between one of the electrodes 2| and the electrode I08 is sufliciently great to produce a discharge across the gap 2i, the point 20 will then be grounded by the arc across this gap and the generator will be discharged the same as if the point were grounded by operation of the solenoid 81 in Fig. 1. The precipitating voltage between the electrodes 2| and I08 will be the sum of the voltages due to the charge on the impulse generator and the 60 cycle voltage impressed through the transformer winding H0. This voltage of course will be a maximum at the crest of the wave of the 60 cycle voltage so that discharge will take place on the crest of the wave or very close to the crest of the 60 cycle wave, as required by standards for this form of test.

We claim:

1. In combination a capacitor unit having one 1 terminal insulated from ground and having the other terminal thereof connected to ground through an impedance having a time constant, means for charging said unit and means for connecting said insulated terminal to ground while said unit retains its charge to shift the potential of the other said terminal momentarily away from ground potential due to the charge in said unit.

'2. In combination a pair of capacitor units connected in series, the connected electrodes of said units being connected through impedance to ground, a discharge circuit to ground connected to one terminal of said series, the other terminal of said series being insulated from ground, the circuit through said impedance to ground having a greater time constant than that of said discharge circuit to ground, means for charging said capacitors, and means for grounding said insulated terminal to impress momentarily substantially the combined voltages of said capacitor units on said discharge circuit. v 3. In combination a pair of capacitor units connected in series, an impedance connected at one end thereof to the joined electrodes of said capacitor units and having the other end thereof grounded, means for charging said capacitors so that one terminal of said series will be below and one aboveground potential, a discharge circuit to ground connected through an arcing gap to one terminal of said series, said discharge circuit having a lower time constant than that of said impedance, and means for grounding the other terminal of said series to shift the potential of said joined electrodes away from ground potential and impress the combined voltages of said units on said discharge circuit.

4. An impulse generator comprising a plurality of groups of capacitors connected in parallel and having a series discharge path, one of said groups being grounded through impedance at an intermediate point in said group, means for charging said capacitors, and means for grounding one end of the group having an intermediate point grounded, to shift momentarily the potential of said intermediate point away from ground potential.

5. In combination a plurality of capacitor units, :means for connecting said units in series, one end of said series being connected through impedance to ground, means for charging said units so that when said units are connected in series the other end of said series will have difference in potential from ground substantially equal to the combined voltages of all of said units, an additional capacitor unit having one terminal insulated from ground and having its other terminal connected to the end of said series between said series and said impedance and means for grounding said insulated terminal to add the voltage of said additional capacitor to that of said series.

6. An impulse generator comprising a plurality of capacitors, arcing gaps separating said capacitors into groups but arranged to connect said groups in series to provide a series discharge path for said capacitors when said gaps are bridged by discharge arcs, conductors connecting said groups in parallel for chargingsaid capacitors, said conductors having suflicient impedance therein to impart a greater time constant to the parallel circuit connecting said groups than that of said series discharge circuit, one of said groups being grounded through impedance at an intermediate point in said group, and means for grounding said group at one end thereof to shift, momentarily, the potential of said intermediate point away from ground potential.

7. An impulse generator comprising a pluralityof groups of capacitors, arcing gaps between said groups for connecting said groups in series to provide a series discharge path for said generator, an intermediate point of the endmost group of said capacitors being connected through an impedance to ground, the endmost terminal of said group being normally ungrounded, and means for grounding said endmost terminal to impress the entire voltage of said end group on the arcing gap next adjacent thereto to precipitate series discharge of said capacitors, the time constant of the ground connection for the intermediate point of said endmost group being approximately ten times that of the series discharge circuit of said generator.

8. An impulse generator comprising a plurality of capacitors, arcing gaps connecting said capacitors in series and forming a series discharge circuit for said generator, there being a pair of capacitor units between said end and the next adjacent arcing gap in said series circuit, a point in the circuit between the capaci or unitsof said pair being grounded through an impedance, said impedance being great enough to cause substantially the combined voltage 01 said pair of capacitor units to be momentarily impressed upon said next adjacent arcing gap in said series circuit when the endmost terminal of said series circuit is grounded, and means for grounding said endmost terminal.

9. An impulse generator comprising a plurality 01' groups of capacitors, the endmost one 01 said groups comprising a pair of capacitor units, arcing gaps interposed between said groups to provide a series discharge circuit for said generator, a point in the connection between the capacitors of the endmost group being grounded through an impedance, means for grounding at the will of the operator the endmost terminal of said endmost group, the grounding connection of said intermediate point having a time constant approximately ten times that of the series discharge circuit of said generator so as to impress the combined voltage of the endmost group of capacitors on the adjacent arcing gap to precipitate discharge of said series circuit when the endmost terminal of said series circuit is grounded.

10. An impulse generator comprising a plurality of groups of capacitors, arcing gaps for connecting said groups in series to provide a series discharge path for said generator, one endmost group of said series comprising a pair of units, an intermediate point in the connection between said pair of units being grounded through an impedance, means for charging said groups in parallel comprising a circuit having impedance therein suificient to impart to said circuit a time constant approximately ten times that of the series discharge circuit formed by said arcing gaps, the impedance in the connection to ground of the intermediate point of said endmost group having a time constant approximately ten times that of the discharge circuit of said groups, and means for grounding the endmost terminal of said endmost group at the will of the operator to impress the combined voltage of the pair of capacitors in said endmost group upon the adjacent arcing gap to precipitate discharge of said generator.

11. An impulse generator comprising a plurality of capacitors having a parallel charging circuit and a series discharge circuit, and means to precipitate series discharge of said capacitors, said means comprising a pair of spaced elec trodes for grounding one end of the series discharge circuit, and a remote control device for moving said electrodes together.

12. An impulse generator comprising a plurality of capacitors having a parallel charging circuit and a series discharge circuit and means to precipitate series discharge of said capacitors, said means comprising a pair of spaced electrodes, and means for inducing a discharge between said electrodes to provide a conducting path between said electrodes from one end of the series discharge circuit to ground.

13. An impulse generator comprising a plurality of capacitors, arcing gaps separating said capacitors into groups and adapted to connect said groups in series when discharge occurs across said gaps, one endmost group of said series comprising a pair of capacitor units, an intermediate point in the connection between the units of said pair being grounded through an impedance having a time constant greater than the series discharge path of said generator, means for grounding the endmost terminal of said endmost group, said grounding means comprising a pair of spaced electrodes, one of which is connected to said endmost terminal and the other of which is grounded, and electrically controlled means for electrically connecting said terminals.

14. An impulse generator comprising a plurality of capacitors connected in series, a point between two of said capacitors being grounded through an impedance having a time constant greater than the time constant of said series circuit, an oscillograph for recording the characteristics of the discharge impulses of said generator, and means for connecting said oscillograph with said intermediate grounded point in said genera tor circuit to precipitate operation of said oscillograph when discharge of said generator occurs.

15. An impulse generator comprising a plurality of capacitors having a series discharge circuit including arcing gaps connecting said capacitors in groups, an intermediate point of the endmost group at one end of said series of capacitors being grounded through an impedance having a time constant greater than that of the series discharge circuit of said generator, means for grounding the endmost terminal of said endmost group to precipitate discharge of said series circuit, an oscillograph for registering the characteristics of the discharge impulses of said circuit, and means electrically connected with said intermediate grounded point for initiating operation of said oscillograph.

16. An impulse generator comprising a plurality of capacitors, arcing gaps separating said capacitors into groups and adapted to connect said groups in a series discharge circuit when discharge occurs across said gaps, an intermediate point in the endmost group at one end of said series of capacitors being grounded through an impedance having a time constant greater than the time constant of said series discharge circuit, means for charging said groups in parallel, said charging means comprising a circuit having impedance therein to impart to said charging circuit a time constant greater than the series discharge circuit of said groups, means for grounding the endmost terminal of said endmost group to raise momentarily the voltage of the point in said endmost group connected to said grounding impedance, an oscillograph for recording the characteristics of the discharge impulse of saidgenerator, and means electrically connected to the intermediate grounded point of said endmost group for precipitating operation of said oscillograph.

17. An impulse generator comprising a plurality of groups of capacitors, a parallel charging circuit for said groups, a series discharge circuit for said groups, an oscillograph for registering the characteristics of the discharge impulse of said generator, and a common device for precipitating discharge of said generator and for instituting operation of said oscillograph, the discharge circuit of said generator having suificient time lag to insure operation of said oscillograph at the time of discharge of said generator.

18. An impulse generator comprising a plurality of capacitors, arcing gaps separating said capacitors intogroups and providing a series discharge path for said groups when arcing occurs across said gaps, an oscillograph for registering the characteristics of the discharge impulse of said generator, and means for precipitating discharge of said generator and for instituting operation of said oscillograph, the electrodes of one of said arcing gaps having a size and spacing to impose a time lag between the operation of said discharge precipitating means and the discharge of said generator to insure operation of said oscillograph prior to discharge of said generator.

i19. An impulse generator comprising a plurality of capacitors, arcing gaps separating said capacitors into groups and adapted to connect said groups in series when arcing occurs across said gaps, the terminals of one of said gaps having characteristics similar to a rod gap to impose a time lag in the discharge of said generator, and a capacitor interposed between one of said terminais and ground to maintain a substantially constant potential of said terminal relative to ground during the time lag caused by said gap.

20. An impulse generator for impressing impulse voltage on a test piece, said generator comprising a plurality of capacitors, arcing gaps separating said capacitors into groups and adapted to connect said capacitors in series when discharge occurs across said gaps, an arcing gap interposed between one terminal of said series and ground, and means for inducing discharge across said arcing gap to ground said terminal and precipitate discharge of said generator, said last named means comprising a source of alternating current, means for connecting said source of alternating current with said test to impress on said test piece alternating voltage from said source, and means for gradually charging the capacitors to raise the voltage thereof to a point where discharge will occur across said grounding gap on the crest 01' a wave impressed upon said gap by said source of alternating current.

HAROLD L. RORDEN. PAUL M. ROSS. 

